The explanation, it turned out, is that one side of the ancient pass was provided by the cliffs which still loom above the Leonidas Memorial, but the other side was the Gulf of Malia, which with the passing of the centuries has retreated by 9km, transforming a narrow coastal track into a broad plain covered with rice fields.
With the sea on one side - guarded by the Athenian fleet - and seemingly impassable mountains on the other, the Persians couldn't bring their superior numbers to bear and so for two days the Greeks under Leonidas kept them at bay. On the third day, however, a traitor told Xerxes of a pass through the mountains, the Greeks were surrounded, and the battle was lost.
Most of the Greeks then withdrew. But Leonidas, whose death had been foretold by the Oracle at Delphi, decided to fight on, joined by his 300 Spartans, 700 Thesians and 400 Thebans.
Just over the motorway from the memorial is the small hill where the the Greeks made their last stand. A stone plaque on the Spartan burial mound bears the famous epitaph written by the poet Simonides shortly after the battle: "Stranger, announce to the Spartans that here we lie, having fulfilled their orders."
There's another famous phrase on a plaque under the statue of Leonidas. When Xerxes gave the Greeks a final chance to surrender their weapons Leonidas replied, "Come and get them."
Not far from the statue of Leonidas is a headless bronze statue erected in 1997 in memory of the 700 Thespians who died there. To my surprise, a little further down the road is another memorial, to the 2nd NZEF and the Battle of Crete.
It was a timely reminder that because of the strategic position it occupies - or did until the sea receded - Thermopylae has been the scene of many other battles involving, among others, Greeks, Macedonians, Gauls, Romans, Syrians, Heruli, Bulgars, Byzantians, Turks and Germans and New Zealanders.
The 2nd NZEF memorial was presumably a tribute to the Kiwi troops - including my father - who in 1941 held off the invading German forces long enough to permit the Allied expeditionary force to Greece to be evacuated to Crete.
It's not as famous as the stand taken by Leonidas and his men 2500 years ago but every bit as important.
CHECKLIST
Getting there: Emirates provides daily services from Dubai to Athens with connections from its three daily flights from Auckland. Currently, fares are from $2,765 return (inclusive of all taxes).
Further information: To find out about about touring Greece see Tempo Holidays.
Jim Eagles visited Cape Sounion with help from Emirates and Tempo Holidays.
